% Digital filter Specifications:
wp=0.2*pi;          %                 digital Passband freq in rad
ws=0.3*pi;          %                 digital Stopband freq in rad
Rp=1;               %                 Passband ripple in dB
As=15;              %                 Stopband attenuation in dB
% Analog Prototype Specifications:
T=1;                  %               Set T=1
OmegaP=(2/T)*tan(wp/2);%              Prewarp Prototype Passband freq
OmegaS=(2/T)*tan(ws/2); %             Prewarp Prototype Stopband freq
% Analog Elliptic Filter order calculations:
ep=sqrt(10^(Rp/10)-1);  %             Passband Ripple Factor 
A=10^(As/20);           %             Stopband Attenuation Fator
OmegaC=OmegaP;          %             Analog Prototype Cutoff freq
k=OmegaP/OmegaS;        %             Analog prototype Transition Ratio;
k1=ep/sqrt(A*A-1);      %             Analog Prototype Intermediate cal.
capk=ellipke([k.^2 1-k.^2]);
capk1=ellipke([k1.^2 1-(k1.^2)]);
N=ceil(capk(1)*capk1(2)/(capk(2)*capk1(1)));
fprintf('/n***Elliptic Filter Order=%2.Of\n',N)
% ***Elliptic Filter Order=3
% Digital Elliptic Filter Design:
wn=wp/pi;             %                Digital Passband freq in pi units
[b,a]=ellip(N,Rp,As,wn);
[b0,B,A]=dir2cas(b,a)